1. Technical Field
This invention relates to paper sizing and coating compositions. More specifically, the present invention relates to compositions suitable for use in food packaging and effective over a range of atmospheric conditions.
2. Background Information
Fluorochemicals such as fluorochemical phosphate salts are typically used to provide oil and grease resistance in food packaging application papers, either internally or as paper sizing agents. However, such chemicals tend to be expensive. Further, fluorochemical treatments often have associated toxicity concerns.
Other components also employed as paper coating and sizing agents include gelatins, starches, modified starches and vegetable proteins. However, these components must be used in expensively large amounts in order to impart sufficient oil and grease resistance. These large amounts make the treated paper stiff and/or brittle for many uses. Additionally, papers treated with gelatins and other protein-containing compositions are often undesirably sticky to the touch under hot and humid atmospheric conditions, and unacceptably brittle under dry atmospheric conditions.
Accordingly, there is a continuing need to provide inexpensive paper sizing agents and coatings that are suitable for imparting non-toxic grease and oil resistance over a range of atmospheric conditions.
In an attempt to address the above identified issues of cost, amount and property characteristics in paper sizing, the present invention provides a solution based on a combination of starch and water soluble protein having a bloom strength of above 150 suitable for use in paper sizing. The present invention provides a paper surface sizing that is not sticky to the touch at 50% relative humidity (measured at room temperature). If the starch used in the present invention is non-cationic with an amylose content of less than 40%, paper made with the paper sizing of the present invention also exhibits unexpectedly high oil and grease resistance.
Accordingly, the present invention is directed towards a paper surface sizing composition having at least one starch and a water-soluble protein having a bloom strength of above 150. In particular, the invention includes a paper surface sizing composition having non-cationic starch with an amylose content of less than about 40% by weight and gelatin. Especially useful paper surface sizing agents in the present invention include non-cationic hydrophobically modified starches having an amylose content of less than about 40% by weight and gelatin.
The present invention also provides a method of using the above described paper sizing composition to provide oil and grease resistant paper, the process of preparing the paper, and papers prepared thereby.
Finally, the paper sizing agents of the present invention can be used in a sufficiently small quantity that provides an inexpensive paper of acceptable flexibility and that is not sticky, particularly under hot and humid conditions.